1. Field of the Invention
The present invention belongs to a technical field for inspecting a printed circuit board (hereafter referred to as “component mounting substrate” or simply referred to as “substrate”) with components mounted. Particularly, the present invention relates to a method for performing inspection on whether a correct component is mounted on a substrate to be inspected and an apparatus having a function of executing the inspecting method.
2. Description of Prior Art
A component mounting machine referred to as “mounter” has been used so far in order to automate high-density component mounting. A plurality of component supplying devices respectively referred to as “feeder” is set on the mounter. Each feeder holds many same types of components and is managed in accordance with a specific identification number referred to as “feeder number”.
Data showing that the component of which feeder is mounted on which substrate (generally referred to as “mount data”) is previously entered in the controlling section of the mounter. The mount data is generated in accordance with CAD data for designing a substrate, in which data values including the mounting position, height, and feeder number of a feeder serving as a component supplying source are set for each component. The controlling section controls a head portion for mounting a component in accordance with the mount data and takes out a component from a feeder corresponding to each mounting position and then, sets the component to a corresponding mounting position.
A tape feeder widely used for this type of mounter uses a reel on which a tape housing many components is wound. The reel is removal. When a tape runs out, an old reel is properly replaced with a new reel. Moreover, when a component to be mounted is changed in accordance with the change of a substrate to be fabricated, the reel is replaced with a reel for housing the changed component.
Thus, a component mounting machine makes it possible to automatically mount a component adapted for the mounting position of each component in accordance with mount data. However, processing of replenishing component to a feeder or replacing components in the feeder in accordance with the change of substrate to be fabricated is performed by man power. Therefore, when a person in charge supplies an incorrect component, it is impossible to supply a correct component to subsequent substrate and thus, a defective substrate is produced.
To detect a component mounting error due to the above human error, inspection for determining whether each component is a correct component is conventionally executed in a substrate inspecting apparatus for inspecting a component mounted state (in this specification, the above inspection is referred to as “mounting error inspection”). The mounting error inspection determines whether a character string in an image obtained by imaging a component by a video camera coincides with a previously enter correct character string by noticing that a character string showing the type of a component or the like is printed on the body of the component. Specifically, a method of performing pattern matching between the above image and the image of a correct character string and a method of applying character recognition to the image and collating the recognized character string with an entered character string are executed.
However, because these methods respectively requires a lot of time for processing, when executing inspection for each component on every substrate, a large amount of time is necessary for the inspection.
Moreover, this type of determination processing is easily influenced by a very small foreign matter, character bleeding, chip, or change of font. Therefore, even when a character string is proper, it may be determined that the character string is improper. Therefore, the so-called disinformation occurs that no-good determination is output in spite of a good component and moreover, a problem occurs that the accuracy and efficiency of the inspection are extremely deteriorated.
Japanese Patent Laid-Open Publication No. 2002-183712 is present as the prior art for decreasing the number of erroneous recognitions. In the case of this patent document, when comparing a character string extracted from the image of a component with an expected character string to be recognized, it is recognized that a character string is proper when the number of characters obtained through coincidence determination in the character string becomes a predetermine number or more.
However, even by using the method disclosed in Japanese Patent Laid-Open Publication No. 2002-183712, when a component whose character string is easily erroneously recognized is included in components, it is difficult to lower the frequency at which disinformation occurs.